1. Field of the Invention
The present invention pertains to the field of fluid mechanics. It relates to a method of generating a third gas flow of medium pressure and medium temperature, which can be particularly employed as cooling air for a gas turbine, from a first gas flow of high pressure and high temperature.
The invention also relates to an appliance for carrying out the method.
2. Discussion of Background
A particular difficulty associated with the cooling of gas turbines consists in the fact that only a limited number of pressure stages are available on the compressor for the supply of secondary air. Because of this limitation, it frequently happens that cooling air is made available at a very high pressure and that high losses occur before the cooling air reaches a desired pressure level, which may be very much lower than the pressure level at which it is made available. In this case, a further problem consists in the fact that the temperature of the cooling air is very high because simply reducing the pressure does not reduce the stagnation temperature of the cooling air.
A particularly critical situation arises in the case of the low supply pressure level of a compressor when the inlet guide vanes of the compressor are substantially closed. In this case, the low supply pressure, which would be approximately 2 bar with the inlet guide vanes fully open, can fall below the ambient pressure. As a consequence of this, the lowest permissible supply pressure for supplying the bearings with sealing air and the last turbine disk with cooling air would be up to 5 bar, although a positive pressure of 200 mbar would be sufficient.